Biophysical properties of the acetylcholine receptor on clonal myotubes in culture will be determined by analysis of voltage clamped agonist-induced membrane currents. Parameters for receptor activation will be extracted from the measured dose-response relationship. Further experiments will examine the concentration dependence of channel kinetics to aid in distinguishing among possible receptor activation schemes. In additional studies, the functional kinetics of acetylcholine receptors on developing Xenopus muscle cells will be examined to determine the biophysical basis for developmental changes in receptor function. These data are required to form a quantitative picture of acetylcholine receptor function. Such a picture is necessary for understanding chemical synaptic transmission, for interpreting pharmacological data, and for comparison to results of biochemical studies of receptor preparations.